Zavala-Araiza Daniel, Lyon David R, Alvarez Ramón A, Davis Kenneth J, Harriss Robert, Herndon Scott C, Karion Anna, Kort Eric Adam, Lamb Brian K, Lan Xin, Marchese Anthony J, Pacala Stephen W, Robinson Allen L, Shepson Paul B, Sweeney Colm, Talbot Robert, Townsend-Small Amy, Yacovitch Tara I, Zimmerle Daniel J, Hamburg Steven P
Environmental Defense Fund, Austin, TX 78701;
Carbon Now Cast, LLC, State College, PA 16802;
Proc Natl Acad Sci U S A. 2015 Dec 22;112(51):15597-602. doi: 10.1073/pnas.1522126112. Epub 2015 Dec 7.
Published estimates of methane emissions from atmospheric data (top-down approaches) exceed those from source-based inventories (bottom-up approaches), leading to conflicting claims about the climate implications of fuel switching from coal or petroleum to natural gas. Based on data from a coordinated campaign in the Barnett Shale oil and gas-producing region of Texas, we find that top-down and bottom-up estimates of both total and fossil methane emissions agree within statistical confidence intervals (relative differences are 10% for fossil methane and 0.1% for total methane). We reduced uncertainty in top-down estimates by using repeated mass balance measurements, as well as ethane as a fingerprint for source attribution. Similarly, our bottom-up estimate incorporates a more complete count of facilities than past inventories, which omitted a significant number of major sources, and more effectively accounts for the influence of large emission sources using a statistical estimator that integrates observations from multiple ground-based measurement datasets. Two percent of oil and gas facilities in the Barnett accounts for half of methane emissions at any given time, and high-emitting facilities appear to be spatiotemporally variable. Measured oil and gas methane emissions are 90% larger than estimates based on the US Environmental Protection Agency's Greenhouse Gas Inventory and correspond to 1.5% of natural gas production. This rate of methane loss increases the 20-y climate impacts of natural gas consumed in the region by roughly 50%.
根据大气数据得出的甲烷排放量估算值（自上而下的方法）高于基于源清单得出的估算值（自下而上的方法），这导致了关于从煤炭或石油转向天然气的燃料转换对气候影响的相互矛盾的说法。基于德克萨斯州巴尼特页岩油气产区一次协调行动的数据，我们发现，在统计置信区间内，总甲烷排放量和化石甲烷排放量的自上而下和自下而上估算值是一致的（化石甲烷的相对差异为10%，总甲烷的相对差异为0.1%）。我们通过重复质量平衡测量以及将乙烷用作源归因的指纹来降低自上而下估算值的不确定性。同样，我们的自下而上估算纳入了比以往清单更完整的设施计数，以往清单遗漏了大量主要排放源，并且我们使用整合了多个地面测量数据集观测结果的统计估计器，更有效地考虑了大型排放源的影响。在任何给定时间，巴尼特地区2%的油气设施占甲烷排放量的一半，高排放设施在时空上似乎是可变的。实测的油气甲烷排放量比基于美国环境保护局温室气体清单的估算值大90%，相当于天然气产量的1.5%。这种甲烷损失率使该地区消耗的天然气对20年气候的影响增加了约50%。
